A symbol is missing in inherited dependencies

[xairy]

Hi,

The documentation for the referenced field of the Symbol class says that it includes dependencies inherited from surrounding menus and if's.. However when I look at the value of the referenced field for COMEDI_NI_USB6501 (source), I don't see the USB symbol there:

> print(kconf.syms['COMEDI_NI_USB6501'].referenced)
set([<symbol COMEDI_USB_DRIVERS, tristate, "Comedi USB drivers", value m, user value m, visibility m, direct deps m, drivers/staging/comedi/Kconfig:1183>, <symbol COMEDI, tristate, "Data acquisition support (comedi)", value m, user value m, visibility y, direct deps y, drivers/staging/comedi/Kconfig:1>, <symbol STAGING, bool, "Staging drivers", value y, user value y, visibility y, direct deps y, drivers/staging/Kconfig:1>])

COMEDI_NI_USB6501 depends on COMEDI_USB_DRIVERS through an if, and COMEDI_USB_DRIVERS in turns depends on USB through a depends on. So AFAIU USB should be in referenced.

Is this a bug or there's something I misunderstand?

Thanks!

[ulfalizer]

Hello,

referenced isn't transitive. It only includes "direct" references.

The reason dependencies from surrounding ifs and menus count as direct references has to do with dependency propagation. Basically, if FOO is just a shorthand for adding depends on FOO to each item within the if, and a depends on on a menu also gets propagated to all the items in it.

These two ways of defining two symbols A and B are equivalent:

With if:

if B

config A
	bool

endif

if C

config B
	bool

endif

With depends on:

config A
	bool
	depends on B

config B
	bool
	depends on C

In both cases, A ends with just B in referenced, and B ends up with just C.

To get transitive references, you'll have to calculate the transitive closure (I think that's the term...), recursively expanding the .referenced until no new symbols appear.

If you're only interested in the direct dependencies of a symbol (its depends on, possibly inherited), have a look at Symbol.direct_dep btw. You can extract all the symbols in it with the global expr_items() function.

[xairy]

Ah, OK, I see. Maybe it makes sense to mention this in the documentation? The word inherited seems confusing to me here. Thanks!

[ulfalizer]

Clarified the docstring and added some more details in 814e2de. Does it look okay?

[xairy]

Looks good, thanks you!